Prosthetic heart valve

ABSTRACT

Bi-leaflet heart valves have improved flow characteristics in their open position as a result of employing valve bodies of elongated axial dimension. By elongating the axial dimension of valve bodies which have straight, smooth interior wall surfaces oriented parallel to the centerline through the valve and to the flow path of blood, and by employing a pair of occluders which have major surfaces that are rectilinear and can assume an orientation that is substantially parallel to the centerline in the open position, a streamlining of blood flow occurs. The pivot arrangements avoid the use of acute angular surface orientations and cause the occluders, although aligned substantially parallel to blood flow in the open position, to promptly pivot toward the closed position upon reversal of blood flow. This streamlining substantially reduces turbulence and results in low head loss, both significant advantages in bi-leaflet heart valve performance.

BACKGROUND OF THE INVENTION

The present invention pertains to heart valve prostheses and inparticular, to prosthetic bi-leaflet heart valves wherein valve membersgenerally pivot back and forth between open and closed positions.

DESCRIPTION OF THE PRIOR ART

Various types of heart valve prostheses have been developed whichoperate hemodynamically as a result of the pumping action of the heart.Such heart valves include valves having single occluders which pivotalong an eccentric axis (or both pivot and translate), to open and closethe blood flow passageway, such as those described in U.S. Pat. Nos.3,546,711 and 4,725,275. They also include bi-leaflet heart valves, suchas those described in U.S. Pat. Nos. 4,078,268, 4,159,543, 4,178,638,4,308,624 and 4,535,484. The above-mentioned patents illustrate a numberof different arrangements for pivotally connecting valve members (i.e.occluders) to valve bodies. U.S. Pat. No. 3,689,942 to R. K. Rapp showsa heart valve design having a generally square passageway closed by fourpivoted occluders of generally triangular shape; it has a highlyirregular sidewall which creates a lip extending inward that severelyimpedes blood flow.

In recent years, the bi-leaflet heart valve has generally become themechanical valve of choice, and it is now felt that a prosthetic valveshould provide an open position passageway which is large and which hasgood flow characteristics so that blood flows freely therethroughwithout adverse boundary layer separation and with a minimum of drag.Because of the general belief that the shorter the length, the lesswould be resistance to blood flow through the critical region of thevalve, heart valve bodies, and particularly those for bi-leaflet valves,have been designed to be relatively short in axial length. For example,U.S. Pat. No. 3,926,215 issued in 1975 to Macleod, illustrates amechanical check valve having a long tubular body with a frustoconicalinterior passageway wherein an occluder of generally aerofoil shape ispivoted. Although such a valve design is shown in FIG. 1, it isspecifically pointed out in Column 2 of the patent that the illustratedvalve having this tubular valve body is not applicable for use as aprosthetic heart valve by virtue of its proportions. Attention is thendirected to FIG. 3 to show how such a valve body can be longitudinallyor axially shortened to a proportion wherein the longitudinal or axiallength of the valve body is a small fraction of the average diameter ofthe central passageway through the annular valve body. The foregoing hasbeen indicative of the thinking of prosthetic heart valve designers whohave advocated that the length of the valve body should be as short aspossible so as to avoid creating too large a restriction to blood flowthrough the region of the valve. U.S. Pat. No. 4,276,658, shows the St.Jude Medical valve having a scalloped upstream or inflow endarrangement, wherein the pivot recesses are located, with the remainderof the valve body being substantially shorter in length.

Bi-leaflet heart valves have continued to be sought which have improvedflow characteristics in the open position, avoid the likelihood ofclotting, and retain reliability and responsiveness in operation.

SUMMARY OF THE INVENTION

The present invention provides bi-leaflet heart valves of improved flowcharacteristics having valve bodies with substantially smooth sidewallsand a length substantially longer than comparable prior art heartvalves. When such valve bodies are coupled with leaflets that aregenerally pivoted or guided along their lateral edges and that aredesigned so that their outflow and inflow surfaces, in the openposition, can be aligned substantially parallel to the longitudinal axisor centerline of the valve passageway, streamlined flow patterns arecreated past both opposite leaflet surfaces and through the valve body.This desirable streamlining effect is surprisingly achieved by havingthe bi-leaflet valve body proportioned so that its minimum axial lengthis greater than about 50% of the effective diameter of the opening whichconstitutes the central passageway. Preferably, this length is at leastabout 55%, and most preferably at least about 60% of the centralpassageway effective diameter, but usually not greater than about 150%thereof. The leaflets or occluders preferably have bodies ofsubstantially uniform thickness throughout, except for those regionswhere structure responsible for the pivot arrangement may be located.Such occluders are then able to align themselves either substantiallyparallel to blood flow in the open position or to assume an equilibriumposition a few degrees from precise parallel, and this feature, incombination with the elongated, smooth-walled valve body, results instreamlined flow and very low head loss through the valve. Preferablythe axes about which occluders pivot are spaced radially from thelongitudinal axis a distance not greater than about one-half the radiusof the passageway so there is good flow past both surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bi-leaflet heart valve embodyingvarious features of the present invention, shown in its open position;

FIG. 2 is an enlarged cross-sectional view of the heart valve takenalong the line 2--2 of FIG. 1, also showing the valve with the leafletsin their open position, but with the lefthand leaflet shown in elevationinstead of section;

FIG. 3 is a cross-sectional view, reduced in size, similar to FIG. 2 butshowing both leaflets in cross section in their closed position;

FIG. 4 is a fragmentary plan view of the bi-leaflet heart valve shown inFIG. 2 with both leaflets shown in their open position, but without themetal stiffening ring and the sewing ring;

FIG. 5 is a perspective view of an alternative embodiment of a valvebody for a bi-leaflet heart valve embodying various features of thepresent invention with only one of the two occluders installed;

FIG. 6 is a cross-sectional view, enlarged in size, of a heart valveincluding the valve body of FIG. 5 with both occluders installed andshown in the open position;

FIG. 7 is a cross-sectional view of the heart valve of FIG. 6 shown withthe occluders in the closed position;

FIG. 8 is a perspective view of one of the occluders depicted in theheart valve of FIGS. 6 and 7; and

FIG. 9 is an enlarged fragmentary, sectional view taken generally alongthe line 9--9 of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-4 show a prosthetic heart valve embodying various features ofthe present invention. The heart valve 11 is of a bi-leafletconstruction and has particularly improved flow characteristics with itsvalve members in the fully open position. The interior wall of the valvebody 12 is smooth, parallel to blood flow and elongated in axial length,and this feature in combination with the ability of the occluders orvalve members in the open position to assume parallel alignment, i.e.parallel to the centerline or longitudinal axis of the valve passageway,has been found to create a streamlined flow having extremely low loss inhead pressure and minimal turbulence. Although other guide or pivotarrangements for the valve members can be employed, the illustratedarrangement is one that can be used and is described in detail inpending U.S. patent application Ser. No. 674,871, filed Mar. 25, 1991,the disclosure of which is incorporated herein by reference. Anotheruseful pivot arrangement is shown in FIGS. 5-9.

Generally, the heart valve 10 includes a generally annular, elongatedvalve body 12, preferably formed of a pyrolytic carbon-coated graphitesubstrate, in which a pair of generally pivoting occluders or leaflets14 are installed that open and close like a check valve to allow theflow of blood in a downstream direction, as indicated by the arrows 19in FIG. 2, and prevent any substantial backflow in the upstreamdirection. The outer surface of the valve body preferably has a groove15 which receives a metal stiffening ring 16 which in turn is designedto interconnect with and support a sewing ring 18 (see FIG. 2) of aconventional design as well-known in this art.

The blood flow passageway is defined by the interior sidewall or surface20 of the valve body 12, and this surface is smooth and substantiallyparallel to the centerline. By substantially parallel is meant withinabout 3 degrees of true parallel. The passageway is generally thatdefined by a right circular cylindrical surface, which otherwisecylindrical surface is interrupted by a pair of diametrically opposedflat wall sections 24 that constitute the two oppositely facing regionswhere the pivot arrangements are located. As a result of the inclusionof these two flat wall interruptions 24 and the associated pivotprojections, the effective diameter of the passageway, from itsstandpoint of providing a clear channel for blood flow, is reducedslightly as seen in FIG. 4, a fact which is discussed in more detailhereinafter. In the general region of each of these flat wall sections24 is provided a central projection 26 and a pair of upstream flankingprojections 28 which coact to define the generally pivotal or rotativemovement of the leaflets 14 as they move from the fully open position tothe closed position and vice versa.

As best seen in FIG. 1, these sets of projections 26, 28 extendgenerally perpendicularly from each flat wall section 24 of the interiorsidewall. They are clean in outline, being preferably formed to haveonly generally right-angle or obtuse-angle orientations with adjacentsurfaces 20, 24 of the interior passageway through the valve body 12;they are particularly devoid of any acute angle orientations of about70° or less that would provide regions where there would be a highlikelihood of the formation of blood clots. Although the protrusions 26,28 provide minimal obstruction to the flow of blood through thepassageway, even cleaner arrangements could be used, such as that shownin FIGS. 5 to 9, where each of the leaflets is controlled in itsmovement between open and closed positions by a pair of ears protrudingfrom each lateral edge, which ears are received in pairs of elongatedslots provided in the flat wall sections, as described hereinafter.Other suitable guide arrangements can also be used which permit theoccluders or leaflets to assume a substantially parallel orientation inthe full open orientation.

The central projection 26 has a pair of oppositely facing flat surfaces30, each of which is parallel to the valve centerline, and an upstreamsurface 32 which is perpendicular thereto. The edges between these threesurfaces can be faceted or rounded. The central portion of theprojection is relieved by a concave groove 40 which minimizes theobstruction created by the presence of the projection 26 in thepassageway. The projection extends to the downstream end of the valvebody, and its downstream end is rounded. Alternatively, the projectioncan instead be tapered, if desired, for example, at a downstream angleof about 120 to 160 degrees to the flat sidewall section 24 to provide asmooth downstream transition surface.

Each of the flanking upstream projections 28 has a flat surface 42 whichis also oriented parallel to the direction of blood flow, i.e. to thevalve centerline, and each also has a downstream, generallyperpendicular surface 44 and a flat interior wall surface 45 thatextends to the curved interior sidewall of the valve body. The surfaces42 and 44 intersect at what is termed downstream edge 43 of theprojection, which may be faceted or slightly rounded. The interiorsurfaces 45 of the projections are parallel to the flat wall sections 24of the valve body.

The leaflets 14 each have an upstream-facing or inflow surface 46 and anopposed downstream-facing or outflow surface 48, with reference to theleaflets when they are oriented in the closed position (see FIG. 3).Each leaflet thus has two essentially flat surfaces which constitute themajor portion of its body, being only interrupted by lugs which protrudefrom the lateral edges and coact with the projections to guide theopening and closing movements of the leaflets. Accordingly, the majorbody portion of each leaflet is of uniform cross-sectional thickness,and both the inflow surface 46 and the outflow surface 48 can assume analignment substantially parallel to the valve centerline when theleaflets are in the open position (FIG. 2).

Each of the leaflets 14 has a major arcuate edge surface 50, which islocated at its downstream edge, and a minor mating edge surface 52 whichis located at the opposite upstream edge, with respect to the leaflet inits open position. The arcuate edge surface 50 is configured to abut andseat against the smooth cylindrical sidewall 20 of the valve body in theclosed position, whereas the minor mating edge surface 52 is of aconfiguration so as to mate with the corresponding mating edge surfaceof the other of the pair of leaflets. Accordingly, this minor surface 52is flat and oriented at an angle such that the two mating edge surfacesabut while extending diametrically across the valve passageway in theclosed position, as is well known in the art of bi-leaflet valves.

The leaflets 14 each include a pair of opposed lateral edge surfaces 53which lie between the major arcuate surface and the minor mating surfaceand which are preferably flat. The leaflets 14 are proportioned so as toprovide minimal clearance between the flat wall sections 24 of the valvebody and the opposed intermediate lateral edge surfaces 53 so as toenable the leaflets to pivot, with these lateral edge surfaces 53 movingadjacent to the flat wall sections 24 and with one of them usuallyserving as a bearing surface. The projections 26 and 28 are located sothat the surfaces which guide the leaflets in their sliding-pivotalmovement are located within a distance from the centerline plane notgreater than about one-half the radius whereby, in the open position theleaflets are spaced from the centerline plane a distance not greaterthan one-half the radius. By "centerline plane" is meant the planeperpendicular to the flat wall sections 24 which contains thelongitudinal axis or centerline of the valve passageway.

Extending from the outflow surface 48 of each leaflet along its lateraledge is an integral first or opening lug 54, each leaflet having a pairof these lugs 54 which extend toward the centerline plane of the valvein the open position. These lugs have upstream surfaces 52a that arebeveled, i.e. slightly angularly offset from the plane of the minor edgesurface 52; this offset prevents interference with each other duringmovement toward the closed position (see FIG. 3). These lugs 54 havedownstream surfaces 56 oriented to lie in juxtaposition with thetransverse surface 32 of the central projection in the closed position,and these downstream surfaces are preferably oriented at an angle ofbetween about 30 and about 45 degrees to the centerline plane in theopen position. The downstream surfaces 56 are also preferably formedwith a recess 56a which accommodates the rounded edge of the projection26 when in the open position (see FIG. 2); this engagement with theprojection 26 prevents the leaflet from escaping downstream.

Second or closing lugs 57 are also formed in each side section of eachleaflet, as an integral part thereof, which protrude from the inflowsurface 46 of each leaflet along each lateral edge. These second lugs 57have a front camming surface 59 which is arranged so as to lie at adesired acute angle to the plane of the flat surface of the major bodyportion of the leaflet. These closing lugs 57, sometimes referred to asthe inflow surface lugs, have their front camming surfaces 59 orientedat an angle between about 5 degrees and about 35 degrees to thecenterline plane in the open position; they also have a rear angularsurface 61 which is oriented so as to lie generally in juxtapositionwith the transverse surface 44 of the upstream projections 28 when theleaflets are in the closed position.

The radially outer lateral surfaces of the lugs 57 are chamfered neartheir upper ends to provide a small generally triangular surface 63 oneach lug that generally provides clearance when the lug 57 rotates inthe region beyond the flat wall 24 of the valve body. Moreover, thechamfer is precisely located so as to create bearing ears 63a and bwhich can engage the curved sidewall of the valve body along axiallyoriented rub lines during intermediate portions of the closing movementof the leaflets; these bearing ears assist in guiding the rotation ofthe leaflets, particularly after each leaflet has lost sliding contactwith the downstream projection 26 as a result of its being displacedupstream by the reverse flow of blood. The sizing of the leaflets 14 issuch that simultaneous contact between ears along both opposite lateralsides and the interior cylindrical valve body sidewall 20 does notoccur.

The leaflets 14 are installed in the valve body by squeezing the body atdiametrically opposed locations so as to cause the flat wall sections 24to separate further from each other and allow the leaflets to be fittedinto the passageway of the valve body in their operative positions. Theside sections which carry the respective lugs are thus received betweeneach central projection 26 and one of the flanking upstream projections28. When squeezing force is removed, the valve body returns to itsoriginal circular configuration, leaving the desired minimal clearance,with the leaflets being slidably-pivotally mounted for travel betweentheir closed and open positions. The metal stabilizing ring 16 can beappropriately installed, as by shrink-fitting, following theinstallation of the leaflets; however, it may be preferred to firstinstall the metal stabilizing ring which can improve the structuralproperties of a pyrocarbon valve body, the preferred material ofconstruction. The illustrated design allows the leaflets to assume aprecisely parallel orientation in the open position while, assuming thisis the "low energy" or equilibrium position, still assuring that closingmovement of the leaflets begin immediately as flow reversal occurs.

The fully open leaflet position is shown in FIG. 2 wherein the recess56a of the first lug is in contact with the rounded edge between thesurfaces 30, 32 of the central projection and wherein the flat outflowsurface 48 of the leaflet lies in juxtaposition with one of the flankingsurfaces 30 of the central projection so that the leaflets are orientedprecisely parallel to the centerline. Front extensions 57a on theclosing lugs 57 also lie in juxtaposition with the surfaces 42 of theupstream projections 28. As a result, the leaflets create minimalobstruction to the downstream flow of blood, and their locations createregions of very substantial blood flow adjacent both surfaces of eachleaflet as a result of the open leaflet being located a distance fromthe centerline plane not greater than about one-half the radius.

When blood flow reverses as a result of the contraction of the heart,the backflow of blood creates a drag on the surfaces of the leaflets,displacing each leaflet upwardly so that the camming surface 59 of eachclosing lug immediately engages the curved edge of each upstreamprojection 28, causing the leaflet to immediately begin to rotate as itcontinues to slide upward. This prompt rotation continues, exposing theoutflow surface 48 of the leaflet to more and more of the full force ofthe backflowing stream of blood, and thereby amplifying the rotativeforce vector being applied against each leaflet. Rotation andtranslation continues until the leaflets reach the closed position shownin FIG. 3 where they are preferably oriented with their flat main bodysections at an angle of between about 30 and about 45 degrees to thecenterline plane and with the surfaces 56 of the lugs 54 spaced justslightly above, but in juxtaposition with, the upstream transversesurfaces 32 of the central projection 26.

As soon as the next cycle occurs so that there is again a flow of bloodin the normal downstream direction through the valve, the force of bloodon the inflow surfaces 46 causes immediate displacement of the leafletsslightly downward until the surface 56 of the opening lugs contacts thetransverse surface 32 of the center projection. This causes pivoting ofthe leaflets toward the open position to quickly occur, with suchpivoting being primarily guided by the engagement between the surfaces56 and 56a of the opening lugs with the center projection 26. Rotationcontinues until the open position is reached, wherein the leaflet or athin extension 54a of the lug 54 is in contact with the surface 30, andthe leaflets can assume this precise parallel position with respect tothe valve centerline or, depending upon the blood flow pattern in theheart at that instant, can assume a low energy or equilibrium positionthat may be a few degrees short of parallel. In the open position, therounded upstream edges of the projection 26 interengage with and arereceived within the recesses 56a, and the front extensions 57 a of thesecond lugs 57 lie adjacent or engage the surfaces 42 of the projections28.

It has been found that by proportioning the valve body so that it iselongated in length with respect to the diameter of the centralpassageway, unexpected advantages occur in a prosthetic heart valvewhere the occluders are aligned substantially parallel to the flow ofblood through the valve in the open position and the sidewall of thevalve body is smooth and substantially parallel to the centerline. Thevalve body sidewall that defines the blood flow passageway should befree of surfaces oriented at an acute angle of about 70° or less to eachother also free of any generally upstream oriented surfaces. Preferably,there are no surfaces oriented so that they could potentially createturbulence and/or provide regions where there would be a high likelihoodof clotting. It was found that, by appropriately elongating the valvebody so that the minimum axial length at any location about theperiphery of the interior passageway meets the aforementioned criterion,the relatively elongated length of the valve body causes a streamlinedblood flow to be created which results in unexpectedly low head lossacross the valve and minimal turbulence. Another significant advantagewhich arises from this construction is the ability to design the valveso that the amount of angular rotation through which the leaflets travelcan be reduced, if desired, by having the leaflets reach the closedposition oriented at a downstream angle to the centerline of as low asabout 35°, usually between about 35° and 45°. Generally the lower theamount of angular rotation is, the more quickly the valve will close,and the less be the volume of blood which regurgitates.

More specifically, the valve body 12 has a very slightly roundedentrance edge 71 and a very slightly rounded exit edge 73; accordingly,the length L of the valve body 12 in the axial direction is measured asshown on FIG. 2 and covers the entire straightline section of theinterior sidewall. The illustrated valve body 12 is of uniform axiallength about its periphery; however, if the valve body were scalloped orotherwise shaped to have a varying axial length at certain locations, itwould be the minimum axial length which is considered to be importantbecause of the effect that such variance in length about the peripheryof the passageway has on the streamlining of the blood flow pattern.

If the valve body 12 had an interior passageway which was that of atotal right circular cylinder, then the effective diameter of thepassageway would be the actual interior diameter D of the valve bodyopening. However, as indicated above and best seen in FIG. 4, the valvebody 12 has a pair of diametrically opposed flat wall sections 24 and isalso narrowed further in these locations by the presence of theprojections 26 and 28. In this instance, an appropriate value, which isreferred to as the effective diameter D', is calculated that is equal tothe diameter of a circle having the same cross-sectional area of theopen region of the valve body central passageway. Calculations show thatflat sections 24 of the proportions seen in FIGS. 1 and 4 only reducethe cross-sectional area through the valve body by about 4%; accordinglyfor valve bodies of such generally circular cross section, the axialminimum length is preferably equal to at least about one-half of theinterior diameter. The presence of the projections 26, 28, which extendinward from the flats 24, further reduce the open region so that it isonly equal to about 93% of the complete circle. Accordingly, for aprosthetic heart valve 10 having a nominal interior diameter of 0.935inch, the effective diameter (reduced for the presence of the flats andthe projections) would be about 0.903 inch, about 96.5%. Preferably, thevalve body is constructed so that it has an effective diameter D' equalto at least about 95% of the nominal interior diameter D, i.e. thediameter measured parallel to the two flat wall sections.

It has been found that such improved flow characteristics through theopen valve are achieved in a valve body having the aforementionedcharacteristics, when the occluders are substantially parallel to bloodflow in the open position and when the ratio of the minimum axial lengthL to the effective diameter D' is at least 0.5:1 and preferably at leastabout 0.55:1 and not greater than about 1.5:1. Most preferably, theratio L to D' should be at least about 0.6:1 to achieve particularlyimproved streamlining and minimum head loss; moreover, to avoid overlylong axial length that may render implantation more difficult, it may bemore preferable that the L to D' ratio is between about 0.6:1 and about1.2:1. In some instances, it is felt most preferable that the L to D'ratio is between about 0.6:1 and about 1:1. By designing the valve bodyto fall within these criteria and to have an interior wall surface ofthe aforementioned characteristics, and by employing a pair of occludersthat are substantially uniform in thickness and have inflow and outflowsurfaces that can be aligned substantially parallel to the centerline inthe open position and are mounted so there is substantial blood flowpast both the outflow and inflow occluder surfaces, unexpectedstreamlining of the flow patterns through the valve passageway isachieved that provides important performance advantages including asubstantial reduction in head loss and turbulence compared, for example,to commercially available bi-leaflet valves having an L to D' ratio ofabout 0.25:1.

Shown in FIGS. 5-9 is an alternative embodiment of a bi-leaflet heartvalve 131 which also incorporates an elongated valve body construction132; it employs a pair of curved leaflets 133 and a different type ofpivot mechanism, but one which also allows the leaflets to assume anorientation in the open position with their rectilinear surfacesparallel to the centerline of the valve and thus substantially parallelto the flow of blood through the valve. The heart valve 131 has a pairof leaflets 133, each of which has a convex inflow surface 135 and aconcave outflow surface 137, these rectilinear surfaces form the mainbody portion of the leaflet which has a sidewall of uniform thicknessexcept for the two regions along the lateral edges where there is aslight thickening to create a pair of flat surface sections 139 fromwhich a pair of ears or bosses 141 protrude, which coact to define thepivoting-sliding motion of the leaflets. In essence, therefore, eachleaflet 133 is generally a section of a tube or hollow cylinder ofelliptical or oval cross-section, as perhaps best seen in FIG. 8, andhas a flat upstream mating edge 138 and a downstream arcuate edge 138a.As a result of this construction, as shown in FIG. 6, the valve 131 inits open position has an enlarged central flow channel, compared to thevalve 10 where two flat leaflets are employed.

The valve body 132 is again elongated in axial length, having an axialdimension equal to about 60 percent of the effective internal diameterof the valve body. The annular valve body 132 is essentially that of ahollow right circular cylinder again having a groove 143 in its exteriorsurface designed to accommodate a metal stiffening ring 145; thestiffening ring 145, shown installed in FIGS. 6, 7 and 9, as discussedhereinbefore is used for the attachment of a standard sewing ring (notshown) to the valve as well known in this art. An otherwise cylindricalinterior sidewall surface 147 of the valve body 132 is interrupted by apair of diametrically opposed flat wall sections 149, all of which aresmooth and parallel to the centerline through the valve body. Two pairsof relatively shallow slots 151, 153 in each of the flat wall sectionsreceive the ears 141 on the leaflets and coact therewith to define themovement of the leaflets between the open and closed positions. As bestseen, perhaps, in FIG. 9, the ears 141 which project from the sidesections 139 of the leaflets are spheroidal in shape, being illustratedas hemispheres of a curvature that essentially matches the radius ofcurvature of the shallow slots 151 and 153; the slots have a justslightly greater radius of curvature to assure there will be smoothmovement of the ears within the slots.

In the open position illustrated in FIG. 6, the leaflets 133 are locatedat the downstream end of both slots 151, 153, with normal blood flowthrough the valve being in the downstream direction of the arrows B.Although the leaflets are curved in profile, their main body surfacesare rectilinear, i.e. made up of a locus of straight lines which extendparallel to the centerline of the valve in the open position, andprovide minimal resistance to blood flow in the downstream direction. Assoon as blood flow reverses, the leaflets 133 are displaced upstream intranslational movement guided by the coaction of the spherical ears 141in the pairs of slots 151, 153.

As can be seen in FIGS. 6 and 7, the upstream slots 151 are straight andparallel to the centerline of the valve passageway. The downstream slotsare also straight, but are oriented at an upstream angle of about 35° tothe orientation of the upstream slots and also to the valve centerlineplane, the orientation being such that the slots 151, 153 diverge fromeach other in an upstream direction. Therefore, as upstream displacementof the leaflets occurs, although the ears 141a can move directlyupstream in the upstream slots, the simultaneous movement of the ears141b in the oblique slots 153 causes pivoting of the leaflets toimmediately begin because the ears in the slots 153 are being forcedaway from the centerline plane while the sidewalls of the slots 151restrain the ears 141a therein from any movement but that in an axialdirection. As can be seen from FIGS. 6 and 7, the length of the obliqueslots 153 is longer than the slots 151 which are parallel to thecenterline. Accordingly, the ears 141b travel farther than do the ears141a as the upstream movement continues; this movement is in the form ofa pivoting motion about the ears 141a, which ears themselves are alsomoving upstream in the valve body as this pivoting of the leaflet isoccurring. About the time the ears 141a reach the upstream ends of theslots 151, the flat surfaces of the mating edges 138 of the leafletsabut each other, and the arcuate downstream edges 138a of the leafletsabut the right circular cylindrical interior sidewall 147 of the valvebody to provide a seal about the periphery of the leaflets in thisregion. The ears 141b preferably halt just short of the upstream ends ofthe slots 153. As in the case of the other leaflets hereinbeforedescribed, the proportioning is such that the flat side sections 139 ofthe leaflets are located in essentially sliding contact with the flatinterior wall sections 149 of the valve body, thus providing bothbearing surfaces and seals in these regions.

When normal blood flow resumes, downward displacement of the leaflets132 causes such sliding-pivoting action to be carried out in the reversedirection, again guided by the sliding engagement of the ears 141b alongthe downstream edges of the oblique slots 153 and of the ears 141a inthe parallel slots 151. This pivoting action continues as the leaflets133 move downward within the valve body 132 from the closed positiondepicted in FIG. 7 to the open position depicted in FIG. 6 wherein bothears are at the bottoms of their respective slots and wherein alignmentof the major surfaces of each leaflet body is precisely parallel to thecenterline. Because the surfaces which define the main body portion ofeach leaflet are oriented substantially parallel to the direction ofblood flow in the open position, the leaflets 133 present minimalresistance to blood flow and, in combination with the elongated valvebody, create the straightened, streamlined flow through the valve with asubstantial reduction in turbulence and head loss as compared tocomparable valves.

In summary, the invention provides bi-leaflet heart valves havingunexpected advantages that result from the creation of streamlined flowthrough the valve because of the elongated parallel, smooth interiorsidewalls of the valve body and the orientation of the leaflets parallelto blood flow through the passageway. The consequence of thisstreamlined flow is substantially reduced turbulence (which is presentlybeing considered to be of more and more importance in the design ofbi-leaflet prosthetic heart valves) and in a very low pressure drop orhead loss across the valve itself, which is particularly advantageous inreducing the amount of work the heart must perform.

Typical peak flow through an aortic prosthetic valve during a cardiaccycle is between about 15 and about 50 liters per minute (lpm) dependingupon the valve size, the heart rate, and the stroke volume or cardiacoutput. For example, a 23 mm diameter valve at 72 beats per minute (bpm)and a 6 lpm cardiac output would have a peak flow of about 30 lpm,whereas, under the same conditions, a smaller 19 mm valve may have apeak flow rate as high as about 40 lpm, which is of courserepresentative of the higher velocity of the blood passing through thesmaller valve opening. Because aortic valves are smaller than mitralvalves, the blood flow (i.e., cardiac output) must traverse the valve ata higher velocity; thus, pressure drop improvement is of particularimportance in aortic valves which are only open about one-half the timethat mitral valves are open as a part of the normal cardiac cycle.

Furthermore, while the foregoing reference was to the peak flow ratethrough an aortic valve, it is important to realize that flow throughaortic valves remains relatively high throughout the major portion ofthe entire pumping cycle. For example, because the forward or pumpingpart of the flow through an aortic valve constitutes only about 35percent of the time of one overall cycle, an aortic valve of about 23millimeters in diameter, in a heart operating at 72 beats per minute andan output of 6 lpm, would have a mean flow rate of about 19 lpm alongwith a peak flow rate of about 30 lpm. Significantly, it has been shownthat in a valve body having an L/D' ratio of about 0.6, the pressuredrop through the valve at a flow rate of about 30 lpm is reduced byabout 28 percent, as compared to a similar valve having an L/D' ratio ofabout 0.3. This alone is an extremely significant improvement inprosthetic valve operating characteristics which is of even moreimportance at higher flow rates where the reduction in pressure drop iseven more striking. However, there are also other features ofsignificantly improved hemodynamic performance that ensue from the useof such a bi-leaflet valve. Lower pressure drops not only mean that lesswork must be done by the heart, but almost as importantly, lowerpressure drops mean lower blood velocities and shear stresses, whichtranslate to reduced blood damage--a significant additional benefit.

Although the invention has been described with respect to a number ofpreferred embodiments, which include the best mode believed by theinventors to create such advantages in improved flow through an openbi-leaflet valve, it should be understood that various changes andmodifications as would be obvious to one having the ordinary skill inthis art may be made without departing from the scope of the inventionwhich is defined by the claims appended hereto.

Particular features of the invention are emphasized in the claims thatfollow.

What is claimed is:
 1. A bi-leaflet prosthetic heart valve whichcomprisesa generally annular valve body having an interior sidewallwhich defines a generally cylindrical central passageway therethroughfor the passage of blood in a downstream direction, said passagewayhaving a longitudinal axis extending in the direction of blood flow andbeing circular in cross section except for a pair of diametricallyopposed flat interior sidewall surfaces, said cylindrical sidewallsurfaces being smooth, straight and parallel to said longitudinal axis,said valve body having means for mounting within a human heart, a pairof leaflets, each having a flat inflow surface and a flat outflowsurface and being of substantially uniform thickness except for regionsalong both opposite lateral edges wherein elements forming a part of apivot arrangement are located, said leaflets being mounted in said valvebody by said pivot arrangement to open and close together to alternatelypermit the flow of blood therethrough past both said surfaces of eachleaflet in a downstream direction when in the open position and blockthe flow of blood in the reverse direction when in the closed position,said valve body and said leaflets being interconnected by said pivotarrangement so that said leaflets are guided in movement between saidopen positions and said closed positions, said pivot arrangement beinglocated along the regions of said flat sidewall surfaces in said valvebody, said leaflets and said pivot arrangement being constructed sothat, when said leaflets are in said open position, both said flatoutflow surfaces and said flat inflow surfaces thereof can assume analignment parallel to said longitudinal axis, with said leaflets eachbeing spaced from said axis by a distance not greater than aboutone-half the radius of said circular passageway, said spacing being suchas to create regions of very substantially blood flow adjacent both saidinflow and outflow surfaces of both leaflets, said pivot arrangementbeing such that from said open position said leaflets translateimmediately upstream and pivoting movement toward said closed positionis positively initiated during each translation as a result of contactbetween each said leaflet and said valve body which applies a cammingforce to each said leaflet, the cross sectional area of said centralpassageway being equal to the area of a circle with diameter D', andsaid valve body being axially elongated so that its minimum axial lengthis such that the ratio of said minimum length to said diameter D' ofsaid central passageway is at least about 0.5:1 and not greater thanabout 1.2:1, whereby normal blood flow through said valve passageway inthe open position is of a streamlined nature, with low turbulence andpressure drop through said heart valve.
 2. A prosthetic heart valveaccording to claim 1 wherein the diameter D' is at least equal to about95% of the diameter of said passageway measured parallel to said flatsidewall surfaces.
 3. A prosthetic heart valve according to claim 2wherein said valve body has a curved entrance edge and a curved exitedge leading toward and away from said interior parallel sidewallsection.
 4. A prosthetic heart valve according to claim 1 wherein saidratio is between about 0.6:1 and about 1:1.